Reducing salt intake with umami: A secondary analysis of data in the UK National Diet and Nutrition Survey

Abstract Reducing sodium content in foods is an important public health measure to reduce salt intake and decrease the incidence of noncommunicable diseases, such as cardiovascular disease and chronic kidney disease. This study quantified the amount of salt intake that could potentially be reduced by using umami substances, including glutamate, inosinate, and guanylate, without compromising taste, for adults in the United Kingdom (UK). We used data comprised of 1834 adults aged 20 years and over from the National Diet and Nutrition Survey (NDNS RP) 2016/2017–2018/2019. Four hypothetical scenarios in which the market share of low‐sodium foods accounts for 0%, 30%, 60%, or 90% of consumed products were considered in the analyses. Per capita daily salt intake corresponding to the NDNS RP food groups was calculated for each scenario, and the salt intake was aggregated by gender and age groups. Replacing salt with umami substances could help UK adults reduce daily salt intake by 9.09%–18.59% (9.21%–18.43% for women; 8.83%–19.43% for men), which is equivalent to 0.45–0.92 g/day of salt reduction (0.41–0.82 g/day for women; 0.50–1.10 g/day for men). The use of umami substances may serve as one method for the UK government to encourage salt intake reduction, particularly in the context of food product reformulation, as 80% of salt consumed in the country comes from processed foods. Empirical studies with sensory evaluation should be conducted to confirm consumer tolerance. The food industry should also be engaged in conversations regarding the addition of umami to food products in the United Kingdom.


| INTRODUC TI ON
In May 2022, 70 health and scientific organizations advocated for sodium (salt) reduction to be made a high global priority and for all nations to develop effective programs to reduce sodium intake to recommended levels (Campbell et al., 2022). High sodium consumption contributes to high blood pressure (Aburto et al., 2013;World Health Organization, 2020), which increases the risk of cardiovascular diseases (Bibbins-Domingo et al., 2010;British Heart Foundation, 2022;Brown et al., 2009;Cogswell et al., 2016;Singh et al., 2013;Thomopoulos et al., 2014), chronic kidney disease (Xie et al., 2016), and gastric cancer (D'Elia et al., 2012;World Cancer Research Fund & American Institute for Cancer Research, 2007). In 2019, approximately 1.9 million deaths worldwide were attributed to a high salt diet (GBD 2019Risk Factors Collaborators, 2020, and the number of deaths increased by 42.8% from 1990 to 2019 (Chen et al., 2021). An estimated 2.5 million deaths could be prevented each year if global salt consumption were reduced to recommended levels (World Health Organization, 2020). Salt intake reduction is also known to be one of the most cost-effective or even cost-saving noncommunicable disease (NCD) control measures (Cobiac et al., 2010).
The reduction of salt intake by 30% between 2011 and 2025 is one of the nine targets in the NCD Global Monitoring Framework initiated by WHO in 2013(World Health Organization, 2014; however, no country has yet to achieve this target to date (Development Initiatives, 2020).
As of 2017, approximately 31% of adults aged 16 years or older in England had high blood pressure, which is the third most common risk factor for premature death and disability in the country (Public Health England, 2020a). The United Kingdom (UK) government initiated a public health campaign to encourage salt intake reduction in the early 1990s. In 2003, the UK Scientific Advisory Committee on Nutrition (SACN) published its report recommending a maximum salt intake of 6 g/day or less for adults (Sutherland et al., 2013), which was comparable with recommendations from WHO (5 g/day) and those from the United States and Canada (5.85 g/day) (Public Health England, 2020a). Following the publication of SACN, the UK government began a program aiming to reduce salt intake across the population (Sutherland et al., 2013).
The UK Food and Standards Agency (FSA) and the Department of Health proposed two strategies to achieve salt intake reduction: (1) a reduction in the salt content of processed foods through engagement with the food industry and (2) an increase in consumer awareness of the impact of salt on health via a public awareness campaign (He et al., 2014). The UK salt reduction strategy was initially successful (Brinsden et al., 2013;Charlton et al., 2014;Gressier et al., 2021;He et al., 2014;Pombo-Rodrigues et al., 2017;Sutherland et al., 2013;Tan et al., 2019), and the mean population salt intake was reduced from 9.5 g/day in 2001 to 8.1 g/day in 2011 (He et al., 2014). However, recent public health policies have had a tendency to focus on sugar and calorie reduction rather than salt. Consequently, the latest trend analyses suggested that there have been no further significant advancement in salt reduction since 2008/2009(Public Health England, 2020a. The mean population salt intake for adults aged 19-64 years was estimated to be 8.4 g/day in 2018/2019, 40% higher than the government recommendation (Public Health England, 2020a), and 68% higher than that of WHO (World Health Organization, 2012). Stronger action is needed to reduce the risk of cardiovascular disease and associated costs for health services and society.
In recent years, the replacement of sodium chloride with "umami" has been discussed as a healthy and natural solution to reduce salt intake while maintaining palatability (Hayabuchi et al., 2020;Nomura et al., 2021;Umeki et al., 2021;Yamaguchi & Takahashi, 1984).
Umami, which is translated as "savory" in Japanese, is induced by monosodium glutamate (MSG) and 5′-ribonucleotides, such as guanosine monophosphate and inosine monophosphate. Even though umami is considered the fifth basic taste sensation, following saltiness, sweetness, bitterness, and acidity (Beauchamp, 2009), few studies have been conducted to empirically evaluate the impact of umami on salt reduction at the population level. Recently, it was reported in Japan that the daily salt intake per adult could be reduced by up to 2.22 g if umami substances were incorporated into selected marketed foods .
In this study, we examined how the use of umami affects the daily salt intake of UK adults using data from the National Diet and Nutrition Survey Rolling Programme (NDNS RP) that is carried out by a consortium comprising NatCen Social Research and the National Institute of Health Research Cambridge Biomedical Research Center (Public Health England, 2020b). The results of this study will serve as men). The use of umami substances may serve as one method for the UK government to encourage salt intake reduction, particularly in the context of food product reformulation, as 80% of salt consumed in the country comes from processed foods.
Empirical studies with sensory evaluation should be conducted to confirm consumer tolerance. The food industry should also be engaged in conversations regarding the addition of umami to food products in the United Kingdom.

K E Y W O R D S
salt, sodium, umami, United Kingdom a first step in considering alternative methods of reducing daily salt intake by addressing upstream food production processes.

| Food and sodium intake data
All individual ingredients of a homemade recipe as reported in the food diary, or components of the purchased product as described on the food packaging, were coded with their respective food codes and linked together under the appropriate Recipe Food Group, which highlights that those food codes were consumed together in one composite dish. The consumed amount of all foods is described in grams.
The nutrient intakes (e.g., sodium) were calculated per 100 g based on the NDNS nutrient databank (NDB), which is populated with information from the UK Composition of Foods Integrated Dataset (Public Health England, 2021b), and is supplemented by the FSA Food Recipes Database (MRC Human Nutrition Research, 2017) and manufacturers' data gathered through food labels and web information. The NDB is updated annually. Each food code in the NDB has a value assigned for 56 nutrients that is further disaggregated into 28 specific food components to ensure accurate reporting of specific food types in the NDNS RP. Each food code is assigned to a food subgroup, expressed as an integer with an alphabetical suffix, which is a food group level of greater detail than the main food groups (Public Health England, 2020b).
In this study, the average intake of each food group and the corresponding sodium intake from the 4-day food diary was calculated and analyzed as a daily value. Salt equivalent intake (g) was defined as sodium (mg) × 2.54/1000. It is important to note that the sampling weight was not applied. This is because we aimed to evaluate the distribution of daily salt intake on an individual basis and to examine how much it would change before and after the incorporation of umami substances (Public Health England, 2021c).

| Sodium reduction rate in various food products with the incorporation of umami substances
We searched PubMed from inception to April 6, 2022 for Englishlanguage articles that estimate the potential sodium reduction rate by using umami substances with the search terms ("sodium intake" OR "salt intake" OR "sodium reduction" OR "salt reduction") AND ("umami" OR "MSG" OR "monosodium glutamate" OR "inosinate" OR "CDG" OR "calcium diglutamate" OR "guanilate" OR "guanylate").
Based on previous studies and input from several food and nutrition experts (coauthors), we estimated salt reduction rates achieved by using umami substances for the NDNS RP food subgroups as listed in Table 1.

| Estimating salt intake reduction with the incorporation of umami substances
As people in the UK already consume a certain amount of lowsodium foods in their daily diets, we set four hypothetical scenarios in which the market share of low-sodium products accounts for 0% (i.e., no low-sodium foods are in the market), 30%, 60%, or 90% of food products.
For each of the major food groups, we calculated the amount of salt that could possibly be reduced for each of the four scenarios by gender and age group (20-29, 30-39, 40-49, 50-59, 60-69, 70-79, and 80+). The salt reduction rate for each NDNS RP food subgroup was expressed as an upper-lower interval in Table 1, representing the range of possible salt reduction rates estimated from the literature. The upper and lower limits were then used to calculate the maximum and minimum possible salt reduction for each food subgroup at the individual level.
The following equations give the upper and lower limits of the j-th food subgroup specific reduction in salt intake by using umami substances in the i-th individual: where S ij refers to the current salt intake of the j-th food subgroup in the i-th participant; U j and L j refer to the upper and lower limits of the sodium reduction rate of the j-th food subgroup, and M k refers to the k-th scenario of the market share of low-sodium consumed products (denoted as M k = 0, 0.3, 0.6 or 0.9 [k = 1, 2, 3 or 4, respectively]).

Upper reduction in salt intake of thejthitem under thekthscenario in theithindividual
Lower reduction in salt intake of thejthitem under thekthscenario in theithindividual

| RE SULTS
The  and men (4.89 g/day). Salt intake tended to be higher among younger than older persons.
The estimated amount of total salt intake reduction for UK adults aged 20 years and over across four scenarios of low-sodium product market shares -0%, 30%, 60%, and 90% -was 0.45-0.92 g/ day, 0.31-0.64 g/day, 0.18-0.37 g/day, and 0.045-0.092 g/day, respectively ( Table 3). Table 4 shows lower-upper mean salt intake reduction rates that could be achieved by incorporating umami substances in food products by gender and age group across the four scenarios. We found that 9.09%-18.59% of salt intake could be reduced by incorporating umami substances into UK adults' diets under Scenario 1. The reduction rates were 6.26%-12.93%, 3.64%-7.47%, 0.91%-1.86% for Scenarios 2, 3 and 4, respectively.

| DISCUSS ION
In this study, we found that it is possible to reduce population-level salt intake among UK adults aged 20 years and over by up to 9.09%-18.59% (9.21%-18.43% for women; 8.83%-19.43% for men), which is equivalent to 0.45-0.92 g/day of salt reduction (0.41-0.82 g/day for women; 0.50-1.10 g/day for men) without compromising palatability by incorporating umami substances into food products.
Our findings regarding salt reduction were comparable or slightly higher than that of a previous study based on US population data that suggested a potential range of salt intake reduction of 5.51%-10.54% (Wallace et al., 2019). The difference in the values of possible salt intake reduction is likely to related to differences in the types of foods consumed in the two countries.
Salt intake reduction has been strongly recommended by WHO to reduce blood pressure and the risk of NCDs (World Health   proportion of adults who generally added salt at the table reportedly decreased from 40.1% in 1997 to 31.7% in 2007 (Sutherland et al., 2013), a more recent study found that the proportion of participants declaring they added salt did not change over time, that is, 50% in year 2008/2009 and 54% in year 2016/2017 (Gressier et al., 2021). On the other hand, several systematic reviews on strategies to improve diets have suggested that food product reformulation would effectively reduce sodium intake (Hyseni et al., 2017;McLaren et al., 2016), and it is estimated that 80% of salt consumed in the UK indeed comes from processed foods (Charlton et al., 2014;Gressier et al., 2021). Thus, it is important for the government to work together with industry to accelerate salt reduction efforts, and the use of umami is one such solution.

TA B L E 3 Estimated salt reduction by scenario and gender (g/day)
Although umami was first discovered by a Japanese scientist (Lindemann et al., 2002), he found the taste in tomato, asparagus, cheese, and meat when he was in Germany (Ninomiya, 2015). There is a variety of free amino acids, umami, found in European soup stocks. Indeed, umami substances can be used to replace salt in various kinds of food and it has been increasingly accepted worldwide (Halim et al., 2020;Jinap et al., 2016;Jinap & Hajeb, 2010;Simões do Couto Rosa et al., 2021). An example of a Western dish that could benefit from salt reduction is chicken pot pie, which invokes a comforting feeling but comes with a hefty amount of sodium. By replacing some of the salt with MSG, the sodium can be reduced by up to 25% while the umami is enhanced (Hedrick, 2022). MSG was once believed to cause side effects, such as headache and nausea.
However, studies have found no consistent clinical data to support these claims (International Glutamate Information Service, 2022a, 2022bMaluly et al., 2017) and the safety of MSG has been approved by official agencies worldwide, including those in Europe (EFSA Panel on Food additives and Nutrient Sources added to Food, 2015).
The salt content of vegetarian and vegan products is found to be higher than regular food products. A study on meat-free alternatives found that the salt content was generally higher than that of meat, and 28% were reportedly even higher than the maximum salt reduction targets (Action on Salt, 2018). It is estimated that 9% of adults in the UK (4.9 million) are vegetarian or vegan, and another 8.8 million plan to go meat free in 2022 (Finder UK, 2022). Precaution should be taken that the mean salt intake estimated in our analysis might be lower than the actual amount. In addition, this study relied on existing literature to derive salt reduction rates by using umami substances. However, the evidence may be insufficient for some food groups. Furthermore, we assumed that the market share of low-sodium food is the same across all food groups due to limited data availability. Divergence of low-sodium product intake, depending on the place where the meal is served or prepared (home or restaurant) was also not considered in this study due to scarcity of data that properly examined these factors. Finally, we were unable to confirm the acceptability of umami substances among UK consumers (Miyaki et al., 2016;. Future studies with sensory evaluation should be conducted to empirically confirm consumer tolerance. The food industry should also be engaged in conversations regarding the addition of umami substances to food products in the UK. This experiment in the UK may help reduce the high-sodium-related burden of diseases around the globe.

| CON CLUS IONS
The incorporation of umami substances into certain foods could potentially reduce population-level daily salt intake in the UK by up to 9.09%-18.59%, which is equivalent to 0.45-0.92 g/day of salt reduction without compromising taste. Although the results of our study should be interpreted with caution as we used food surveys rather than urinary sodium excretion to calculate salt intake, our findings suggest an alternative for the UK government to encourage salt intake reduction during upstream processes such as food production. Additional empirical studies with sensory evaluation should be conducted to confirm consumer tolerance of umami products, and the UK food industry should be engaged in discussions regarding umami's application in food production. Ultimately, the experiment in the UK is expected to help reduce the high sodium-related burden of diseases around the globe.

ACK N OWLED G EM ENTS
None.

FU N D I N G I N FO R M ATI O N
This article was partially supported by a joint research grant from Ajinomoto Co., Inc. H.U. is employed by the commercial funder, Ajinomoto Co., Inc. The commercial funder provided support in the form of salaries for H.U., but did not have any additional role in the decision to publish or the preparation of this manuscript. This article was also partly funded by a research grant from the Ministry of Education, Culture, Sports, Science and Technology of Japan (21H03203).

CO N FLI C T O F I NTE R E S T
K.S. report a grant from the Ajinomoto Co., Inc. H.U. declares that he is employed by Ajinomoto Co., Inc. and has no other competing interests. All other authors declare no competing interests.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data are publicly available at https://beta.ukdat aserv ice.ac.uk/ datac atalo gue/studi es/study ?id=6533 (accessed on June 29, 2022).